Preparation and characterization of erbium and ytterbium co-doped sol–gel SiO2:HfO2 films for planar waveguides

This work reports on the preparation of erbium and ytterbium co-doped SiO2:HfO2 single mode planar waveguides using the sol–gel method. Silica nanoparticles were prepared from tetraethylorthosilicate in basic media and the films were characterized by transmission electron microscopy, scanning electron microscopy, mechanical profilometry, M-lines spectroscopy based on prism coupling technique, X-ray diffractometry, infrared spectroscopy and photoluminescence spectroscopy. The film thicknesses and the refractive indexes were adjusted in order to satisfy a future efficient coupling to single mode optical fiber. Films suitable for both weak and strong light confinement were prepared varying hafnia concentration into the silica matrix . The lifetime values of erbium 4I13/2 state were measured in order to investigate the influence of clustering and hydroxyl groups on the fluorescence quantum efficiency of the 4I13/2 level, responsible for the emission at 1.55 μm attributed to the 4I13/2 → 4I15/2 transition. The high lifetime values suggest the absence of erbium clusters and the elimination of hydroxyl groups by rapid thermal process.